Generally, a mechanical clutch represented typically by a dog clutch or a spline clutch, which establishes clutch engagement through a mechanical interlocking, needs no powers like hydraulic to maintain its interlocked or locked-up state once engaged; therefore, the mechanical clutch transfers the engine power efficiently toward output side. Because of this advantage, such a mechanical clutch has been used for such as a transmission for a passenger car.
The mechanical clutch of this sort requires synchronization of the speed of revolutions of the driving side and the driven side in making them engaged. In a transmission for a passenger car therefore, a synchromesh mechanism using friction on a tapered-cone has been generally used as the synchronizing device. Further to use of such device, an engine revolution control means is provided to regulate the revolution difference between the driving side and the driven side of the clutch to be within a predetermined range so that the gear change shock will be lightened and the clutch breakage will be prevented. Such an automotive twin clutch type transmission as uses such synchromesh mechanism has been described, for example, in the patent literature 1 listed below. As a transmission using a hydraulic friction clutch, which is suitable for a large-sized vehicle like a dump truck, a certain transmission has been described, for example, in the patent literature 2.                Patent Literature 1:                    Japanese Laid-Open Patent Application No. 2008-240832                        Patent Literature 2:                    Japanese Laid-Open Patent Application No. 2007-303519                        